1. Field of This Invention
This invention relates to a process for the separation by extractive distillation of a mixture of chloroacetyl chloride and dichloroacetyl chloride.
2. Prior Art
From U.S. Pat. No. 3,763,023 it has been known to separate chloroacetyl chloride from dichloroacetyl chloride by azeotropic distillation with the help of a hydrocarbon boiling at 90.degree. to 130.degree. C. With diallyl ether, a minimum dichloroacetyl chloride content of 2.1 percent is achieved in the distillate. U.S. Pat. No. 3,763,023 states:
"Operable azeotrope-forming compounds have a boiling point at atmospheric pressure of about 90.degree. to 130.degree. C., preferably about 95.degree. to 120.degree. C., and are hydrocarbons, halogenated by hydrocarbons and aliphatic ethers. A mixture of related compounds such as a saturated aliphatic hydrocarbon fraction having a boiling range within the defined limits can also be used." [Emphasis supplied] [Col. 1, lines 40 to 47]
The use of the term "operable" by such U.S. patent in defining the azeotrope former teaches one ordinarily skilled in the art not to even try similar compounds which have a boiling point outside of the range of 90.degree. to 130.degree. C.
Another process for the production of chloroacetyl chloride is described in German Pat. No. 2,313,405. U.S. Pat. No. 3,950,415 is an English language equivalent of German Pat. No. 2,313,405. A mixture of chloroacetyl chloride and dichloroacetyl chloride is distilled in the presence of water or alkanols with up to 4 carbon atoms. According to Example 1, a content of 2.11 percent by weight of dichloroacetyl chloride is reduced to 1.4 percent by weight; the yield of chloroacetyl chloride amounts to 83 percent by weight. According to Example 2, the dichloroacetyl chloride content is reduced from 1.2 to 0.78 percent by weight, with a yield of chloroacetyl chloride of 85 percent by weight.
In many types of useage of chloroacetyl chloride, a dichloroacetyl chloride content of more than 0.5 percent by weight is disturbing. The known separation processes, for example, that of U.S. Pat. No. 3,763,023, are not capable of producing such pure products and a step-by-step achievement of the required values, for example, according to German Pat. No. 2,313,405, would be achievable (if it were possible at all) only with great loss of chloroacetyl chloride.
See also: Brown, George G., "Unit Operations", John Wiley & Sons, Inc., (1951), pp. 393-394; Gerster, J. A., "Azeotropic and Extractive Distillation", Chemical Engineering Progress, Vol. 65, No. 9 (September 1969), pp. 43-46; Perry (Ed.), "Chemical Engineer's Handbook", 5th Ed., McGraw Hill, pp. 13-43; and Krell, Erich, "Handbuch der Laboratoriumsdistillation", Vol. 1, No. 2, p. 306.